bug5495.sh: Skip test if timeout isn't available

tests/techmap/bug5495.sh

@@ -1,5 +1,10 @@
 #!/usr/bin/env bash
 
+if ! which timeout ; then
+    echo "No 'timeout', skipping test"
+    exit 0
+fi
+
 if ! timeout 5 ../../yosys bug5495.v -p 'hierarchy; techmap; abc -script bug5495.abc' ; then
     echo "Yosys failed to complete"
     exit 1